The connection image quality is a lot related with the application performance (higher quality=lower performance).
The default Image quality is Optimal, because it presents the best cost benefit between quality and performance cost. If you need to have more quality or better performance, take a look on the other options below:
Highest - Works only with PNG images and has no compression (0% compression)
Optimum - Combines PNG and JPEG images (20% compression).
Good - Works only with JPEG images (40% compression)
Fastest - Works only with JPEG images (50% compression).